spamcheck_router:
        no_verify
        check_local_user
        # When to scan a message :
        #   -   it isn't already flagged as spam
        #   -   it isn't already scanned
        condition = "${if and { {!def:h_X-Spam-Flag:}{!eq {$received_protocol}{spam-scanned}}} {1}{0}}"
        driver = accept
        transport = spamcheck

AND

spamcheck:
      debug_print = "T: spamassassin_pipe for $local_part@$domain"
      driver = pipe
      command = /usr/sbin/exim4 -oMr spam-scanned -bS
      use_bsmtp
      transport_filter = /usr/bin/spamc
      home_directory = "/tmp"
      current_directory = "/tmp"
      user = Debian-exim
      group = Debian-exim
      return_fail_output
      message_prefix =
      message_suffix =